Seizures, ataxia, developmental delay and the general paediatrician: glucose transporter 1 deficiency syndrome

The diagnostic and prognostic role of cerebrospinal fluid biomarkers in glucose transporter 1 deficiency: a systematic review

The purpose of this study is to investigate the diagnostic and prognostic role of cerebrospinal fluid (CSF) biomarkers in the diagnostic work-up of glucose transporter 1 (GLUT1) deficiency. Reported here is a systematic review according to PRISMA guidelines collecting clinical and biochemical data about all published patients who underwent CSF analysis. Clinical phenotypes were compared between groups defined by the levels of CSF glucose (≤ 2.2 mmol/L versus > 2.2 mmol/L), CSF/blood glucose ratio (≤ 0.45 versus > 0.45), and CSF lactate (≤ 1 mmol/L versus > 1 mmol/L). Five hundred sixty-two patients fulfilled the inclusion criteria with a mean age at the diagnosis of 8.6 ± 6.7 years. Patients with CSF glucose ≤ 2.2 mmol/L and CSF/blood glucose ratio ≤ 0.45 presented with an earlier onset of symptoms (16.4 ± 22.0 versus 54.4 ± 45.9 months, p < 0.01; 15.7 ± 23.8 versus 40.9 ± 38.0 months, p < 0.01) and received an earlier molecular genetic confirmation (92.1 ± 72.8 versus 157.1 ± 106.2 months, p < 0.01). CSF glucose ≤ 2.2 mmol/L was consistently associated with response to ketogenic diet (p = 0.018) and antiseizure medications (p = 0.025). CSF/blood glucose ratio ≤ 0.45 was significantly associated with absence seizures (p = 0.048), paroxysmal exercise-induced dyskinesia (p = 0.046), and intellectual disability (p = 0.016) while CSF lactate > 1 mmol/L was associated with a response to antiseizure medications (p = 0.026) but not to ketogenic diet.Conclusions:This systematic review supported the diagnostic usefulness of lumbar puncture for the early identification of patients with GLUT1 deficiency responsive to treatments especially if they present with co-occurring epilepsy, movement, and neurodevelopmental disorders. What is Known: • Phenotypes of GLUT1 deficiency syndrome range between early epileptic and developmental encephalopathy to paroxysmal movement disorders and developmental impairment What is New: • CSF blood/glucose ratio may predict better than CSF glucose the diagnosis in children presenting with early onset absences • CSF blood/glucose ratio may predict better than CSF glucose the diagnosis in children presenting with paroxysmal exercise induced dyskinesia and intellectual disability. • CSF glucose may predict better than CSF blood/glucose and lactate the response to ketogenic diet and antiseizure medications.

Creating rare epilepsy cohorts using keyword search in electronic health records

OBJECTIVE

Administrative codes to identify people with rare epilepsies in electronic health records are limited. The current study evaluated the use of keyword search as an alternative method for rare epilepsy cohort creation using electronic health records data.

METHODS

Data included clinical notes from encounters with International Classification of Diseases, Ninth Revision (ICD-9) codes for seizures, epilepsy, and/or convulsions during 2010-2014, across six health care systems in New York City. We identified cases with rare epilepsies by searching clinical notes for keywords associated with 33 rare epilepsies. We validated cases via manual chart review. We compared the performance of keyword search to manual chart review using positive predictive value (PPV), sensitivity, and F-score. We selected an initial combination of keywords using the highest F-scores.

RESULTS

Data included clinical notes from 77 924 cases with ICD-9 codes for seizures, epilepsy, and/or convulsions. The all-keyword search method identified 6095 candidates, and manual chart review confirmed that 2068 (34%) had a rare epilepsy. The initial combination method identified 1862 cases with a rare epilepsy, and this method performed as follows: PPV median = .64 (interquartile range [IQR] = .50-.81, range = .20-1.00), sensitivity median = .93 (IQR = .76-1.00, range = .10-1.00), and F-score median = .71 (IQR = .63-.85, range = .18-1.00). Using this method, we identified four cohorts of rare epilepsies with over 100 individuals, including infantile spasms, Lennox-Gastaut syndrome, Rett syndrome, and tuberous sclerosis complex. We identified over 50 individuals with two rare epilepsies that do not have specific ICD-10 codes for cohort creation (epilepsy with myoclonic atonic seizures, Sturge-Weber syndrome).

SIGNIFICANCE

Keyword search is an effective method for cohort creation. These findings can improve identification and surveillance of individuals with rare epilepsies and promote their referral to specialty clinics, clinical research, and support groups.

One Molecule for Mental Nourishment and More: Glucose Transporter Type 1—Biology and Deficiency Syndrome

Glucose transporter type 1 (Glut1) is the main transporter involved in the cellular uptake of glucose into many tissues, and is highly expressed in the brain and in erythrocytes. Glut1 deficiency syndrome is caused mainly by mutations of the SLC2A1 gene, impairing passive glucose transport across the blood–brain barrier. All age groups, from infants to adults, may be affected, with age-specific symptoms. In its classic form, the syndrome presents as an early-onset drug-resistant metabolic epileptic encephalopathy with a complex movement disorder and developmental delay. In later-onset forms, complex motor disorder predominates, with dystonia, ataxia, chorea or spasticity, often triggered by fasting. Diagnosis is confirmed by hypoglycorrhachia (below 45 mg/dL) with normal blood glucose, 18F-fluorodeoxyglucose positron emission tomography, and genetic analysis showing pathogenic SLC2A1 variants. There are also ongoing positive studies on erythrocytes’ Glut1 surface expression using flow cytometry. The standard treatment still consists of ketogenic therapies supplying ketones as alternative brain fuel. Anaplerotic substances may provide alternative energy sources. Understanding the complex interactions of Glut1 with other tissues, its signaling function for brain angiogenesis and gliosis, and the complex regulation of glucose transportation, including compensatory mechanisms in different tissues, will hopefully advance therapy. Ongoing research for future interventions is focusing on small molecules to restore Glut1, metabolic stimulation, and SLC2A1 transfer strategies. Newborn screening, early identification and treatment could minimize the neurodevelopmental disease consequences. Furthermore, understanding Glut1 relative deficiency or inhibition in inflammation, neurodegenerative disorders, and viral infections including COVID-19 and other settings could provide clues for future therapeutic approaches.

A randomized, double-blind trial of triheptanoin for drug-resistant epilepsy in glucose transporter I deficiency syndrome (Glut1DS)

OBJECTIVE

Evaluate efficacy and long-term safety of triheptanoin in patients >1 year old, not on a ketogenic diet, with drug-resistant seizures associated with Glucose Transporter Type 1 Deficiency Syndrome (Glut1DS).

METHODS

UX007G-CL201 was a randomized, double-blind, placebo-controlled trial. Following a 6-week baseline period, eligible patients were randomized 3:1 to triheptanoin or placebo. Dosing was titrated to 35% total daily calories over 2 weeks. After an 8-week placebo-controlled period, all patients received open-label triheptanoin through Week 52.

RESULTS

The study included 36 patients (15 children; 13 adolescents; 8 adults). A median 12.6% reduction in overall seizure frequency was observed in the triheptanoin arm relative to baseline and a 13.5% difference was observed relative to placebo (p = .58). In patients with absence seizures only (n = 9), a median 62.2% reduction in seizure frequency was observed in the triheptanoin arm relative to baseline. Only one patient with absence seizures only was present in the control group, preventing comparison. No statistically significant differences in seizure frequency were observed. Common treatment-emergent adverse events (TEAEs) included diarrhea, vomiting, abdominal pain, and nausea, most mild or moderate in severity. No serious AEs were considered treatment related. One patient discontinued due to status epilepticus.

SIGNIFICANCE

Triheptanoin did not significantly reduce seizure frequency in patients with Glut1DS not on the ketogenic diet. Treatment was associated with mild to moderate GI treatment-related events; most resolved following dose reduction or interruption and/or medication for treatment. Triheptanoin was not associated with any long-term safety concerns when administered at dose levels up to 35% total daily caloric intake for up to one year.

Metabolic Seizures

Metabolic diseases should always be considered when evaluating children presenting with seizures. This is because many metabolic disorders are potentially treatable and seizure control can be achieved when these diseases are appropriately treated. Seizures caused by underlying metabolic diseases (metabolic seizures) should be particularly considered in unexplained neonatal seizures, refractory seizures, seizures related to fasting or food intake, seizures associated with other systemic or neurologic features, parental consanguinity, and family history of epilepsy. Metabolic seizures can be caused by various amino acids metabolic disorders, disorders of energy metabolism, cofactor-related metabolic diseases, purine and pyrimidine metabolic diseases, congenital disorders of glycosylation, and lysosomal and peroxisomal disorders. Diagnosing metabolic seizures without delay is essential because the immediate initiation of appropriate therapy for many metabolic diseases can prevent or minimize complications.

Genomic Investigation of Infantile and Childhood Epileptic Encephalopathies in Kazakhstan: An Urgent Priority

Objectives: Infantile and childhood epileptic encephalopathies are a group of severe epilepsies that begin within the first year of life and often portend increased morbidity. Many of them are genetically determined. The medical strategy for their management depends on the genetic cause. There are no facilities for genetic testing of children in Kazakhstan but we have a collection of data with already defined genes responsible for clinical presentations.

Methods: We analyzed children with epileptic encephalopathies that began in the first 3 years of life and were accompanied by a delay/arrest of intellectual development, in the absence of structural changes in the brain. Such patients were recommended to undergo genetic testing using epileptic genetic panels in laboratories in different countries.

Results: We observed 350 infants with clinical presentation of epileptic encephalopathies. 4.3% of them followed our recommendations and underwent genetic testing privately. In total 12/15 children became eligible for targeted treatment, 3/15 were likely to have non-epileptic stereotypies/movements, 2/15 were unlikely to respond to any therapy and all had a high chance of intellectual disability, behavioral and social communication disorders.

Conclusion: The genetic results of 15/350 (4.3% of patients) have demonstrated the potential and enormous impact from gene panel analysis in management of epileptic encephalopathy. Availability of genetic testing within the country will improve management of children with genetic epilepsies and help to create a local database of pathogenic variants.

Glut1 Deficiency Syndrome (Glut1DS): State of the art in 2020 and recommendations of the international Glut1DS study group

Glut1 deficiency syndrome (Glut1DS) is a brain energy failure syndrome caused by impaired glucose transport across brain tissue barriers. Glucose diffusion across tissue barriers is facilitated by a family of proteins including glucose transporter type 1 (Glut1). Patients are treated effectively with ketogenic diet therapies (KDT) that provide a supplemental fuel, namely ketone bodies, for brain energy metabolism. The increasing complexity of Glut1DS, since its original description in 1991, now demands an international consensus statement regarding diagnosis and treatment. International experts (n = 23) developed a consensus statement utilizing their collective professional experience, responses to a standardized questionnaire, and serial discussions of wide-ranging issues related to Glut1DS. Key clinical features signaling the onset of Glut1DS are eye-head movement abnormalities, seizures, neurodevelopmental impairment, deceleration of head growth, and movement disorders. Diagnosis is confirmed by the presence of these clinical signs, hypoglycorrhachia documented by lumbar puncture, and genetic analysis showing pathogenic SLC2A1 variants. KDT represent standard choices with Glut1DS-specific recommendations regarding duration, composition, and management. Ongoing research has identified future interventions to restore Glut1 protein content and function. Clinical manifestations are influenced by patient age, genetic complexity, and novel therapeutic interventions. All clinical phenotypes will benefit from a better understanding of Glut1DS natural history throughout the life cycle and from improved guidelines facilitating early diagnosis and prompt treatment. Often, the presenting seizures are treated initially with antiseizure drugs before the cause of the epilepsy is ascertained and appropriate KDT are initiated. Initial drug treatment fails to treat the underlying metabolic disturbance during early brain development, contributing to the long-term disease burden. Impaired development of the brain microvasculature is one such complication of delayed Glut1DS treatment in the postnatal period. This international consensus statement should facilitate prompt diagnosis and guide best standard of care for Glut1DS throughout the life cycle.

A case report of glucose transporter 1 deficiency syndrome with growth hormone deficiency diagnosed before starting ketogenic diet

Background

Growth failure and growth hormone deficiency (GHD) have been reported as one accessory feature of GLUT1 deficiency syndrome (GLUT1DS), considered so far as a long-term adverse effects of ketogenic diet which is used to treat this condition.

Case presentation

We report the case of a 10-year-old Caucasian boy referred for short stature (height − 2.56 SDS) and delayed growth (growth velocity − 4.33 SDS) who was diagnosed with GHD and started treatment with recombinant human growth hormone (rhGH). Because of his history of seizures with infantile onset, deceleration of head growth with microcephaly, ataxia, and moderate intellectual disability, a lumbar puncture was performed, which revealed a low CSF glucose concentration with a very low CSF-to-blood glucose ratio (< 0.4), and genetic tests detected a SLC2A1 gene exon 1 deletion confirming a diagnosis of GLUT1DS. Ketogenic diet was started. After 5.5 years of rhGH treatment his height was normalized (− 1.15 SDS). No side effects were reported during treatment, particularly on glycemic metabolism.

Conclusions

This is the first case of GHD in a Caucasian boy with GLUT1DS diagnosed before starting ketogenic diet, with a good response to rhGH treatment and absence of side effects. We speculate that GHD may represent a poorly recognized clinical feature of GLUT1DS rather than a complication due to ketogenic diet. Under-diagnosis may derive from the fact that growth failure is usually ascribed to ketogenic diet and therefore not further investigated. Pediatric neurologists need to be alerted to the possible presence of GHD in patients with GLUT1DS with slow growth, while pediatric endocrinologist need to refer GHD patients with additional features (motor and cognitive developmental delay, seizures with infantile onset, deceleration of head growth with acquired microcephaly, movement disorder with ataxia, dystonia, and spasticity) that may suggest GLUT1DS.

Incidence and phenotypes of childhood-onset genetic epilepsies: a prospective population-based national cohort

Epilepsy is common in early childhood. In this age group it is associated with high rates of therapy-resistance, and with cognitive, motor, and behavioural comorbidity. A large number of genes, with wide ranging functions, are implicated in its aetiology, especially in those with therapy-resistant seizures. Identifying the more common single-gene epilepsies will aid in targeting resources, the prioritization of diagnostic testing and development of precision therapy. Previous studies of genetic testing in epilepsy have not been prospective and population-based. Therefore, the population-incidence of common genetic epilepsies remains unknown. The objective of this study was to describe the incidence and phenotypic spectrum of the most common single-gene epilepsies in young children, and to calculate what proportion are amenable to precision therapy. This was a prospective national epidemiological cohort study. All children presenting with epilepsy before 36 months of age were eligible. Children presenting with recurrent prolonged (>10 min) febrile seizures; febrile or afebrile status epilepticus (>30 min); or with clusters of two or more febrile or afebrile seizures within a 24-h period were also eligible. Participants were recruited from all 20 regional paediatric departments and four tertiary children’s hospitals in Scotland over a 3-year period. DNA samples were tested on a custom-designed 104-gene epilepsy panel. Detailed clinical information was systematically gathered at initial presentation and during follow-up. Clinical and genetic data were reviewed by a multidisciplinary team of clinicians and genetic scientists. The pathogenic significance of the genetic variants was assessed in accordance with the guidelines of UK Association of Clinical Genetic Science (ACGS). Of the 343 patients who met inclusion criteria, 333 completed genetic testing, and 80/333 (24%) had a diagnostic genetic finding. The overall estimated annual incidence of single-gene epilepsies in this well-defined population was 1 per 2120 live births (47.2/100 000; 95% confidence interval 36.9–57.5). PRRT2 was the most common single-gene epilepsy with an incidence of 1 per 9970 live births (10.0/100 000; 95% confidence interval 5.26–14.8) followed by SCN1A: 1 per 12 200 (8.26/100 000; 95% confidence interval 3.93–12.6); KCNQ2: 1 per 17 000 (5.89/100 000; 95% confidence interval 2.24–9.56) and SLC2A1: 1 per 24 300 (4.13/100 000; 95% confidence interval 1.07–7.19). Presentation before the age of 6 months, and presentation with afebrile focal seizures were significantly associated with genetic diagnosis. Single-gene disorders accounted for a quarter of the seizure disorders in this cohort. Genetic testing is recommended to identify children who may benefit from precision treatment and should be mainstream practice in early childhood onset epilepsy.

Glucose transporter 1 deficiency syndrome: nutritional and growth pattern phenotypes at diagnosis

BACKGROUND/OBJECTIVES

Glucose Transporter 1 Deficiency Syndrome (GLUT1-DS; OMIM #606777) is a rare disease caused by dominant mutations in SLC2A1 encoding GLUT1, which is a ubiquitous transporter of glucose across plasma membranes, particularly across the blood-brain barrier. Hypoglycorrhachia symptoms are the cornerstones of GLUT1-DS, but delayed growth has also been suggested. This led us to investigate, at diagnosis, the relationship between the glycemia/glycorrhachia ratio and the nutritional and growth pattern phenotype of 30 GLUT-DS patients.

SUBJECTS/METHODS

An assessment was made of body weight (BW), body length/height (BL, BH) and body composition by anthropometry and DEXA, and the results put with BL and BW at birth, genetic target, glycemia, insulinemia, and glycorrhachia values.

RESULTS

At birth, 21% of patients had a BW below -1.645 z-score, whereas no patients had BL below the reference values. At diagnosis 23% of the patients had an impaired nutritional status, 19.2% and 3.8% being respectively underweight and overweight/obese; 10%, all under 10 years old, had BL/BH below -1.645 z-score, with no specific features related to body composition. Finally, there was no association between glycemia, glycorrhachia, and growth phenotype.

CONCLUSIONS

GLUT1-DS is associated with impaired BW but not BL intrauterine growth, with a slower than normal pattern of growth rather than growth failure. These data could be useful for the interpretation of any long-term effects of the ketogenic diet, e.g. nutritional and growth pattern decline.

Total Intravenous Anesthesia in GLUT1 Deficiency Syndrome Patient: A Case Report

Patient: Female, 2

Final Diagnosis: GLUT1 deficiency syndrome

Symptoms: Mastoiditis

Medication: —

Clinical Procedure: General anesthesia

Specialty: Anesthesiology

Overall cognitive profiles in patients with GLUT1 Deficiency Syndrome

INTRODUCTION

Glucose Transporter Type I Deficiency Syndrome (GLUT1DS) classical symptoms are seizures, involuntary movements, and cognitive impairment but so far the literature has not devoted much attention to the last.

METHODS

In our retrospective study involving 25 patients with established GLUT1DS diagnosis, we describe the cognitive impairment of these patients in detail and their response to the ketogenic diet in terms of cognitive improvement.

RESULTS

We outlined a specific cognitive profile where performance skills were more affected than verbal ones, with prominent deficiencies in visuospatial and visuomotor abilities. We demonstrated the efficacy of ketogenic diet (KD) on cognitive outcome, with particular improvement tin total and verbal IQ; we found that timing of KD introduction was inversely related to IQ outcome: the later the starting of KD, the lower the IQ, more notable nonverbal scale (verbal IQ correlation coefficient -0.634, p-value = 0.015). We found a significant direct correlation between cognition and CSF/blood glucose ratio values: the higher the ratio, the better the cognitive improvement in response to diet (from T0-baseline evaluation to T1 on average 18 months after introduction of KD-: TIQ correlation coefficient 0.592, p-value = 0.26; VIQ correlation coefficient 0.555, p-value = 0.039). Finally, we demonstrated that a longer duration of treatment is necessary to find an improvement in patients with "severely low ratio."

CONCLUSION

Our results were consistent with the hypothesis that timing of the diet introduction is a predictive factor of cognitive outcome in these patients, confirming that earlier initiation of the diet may prevent the onset of all GLUT1DS symptoms: epilepsy, movement disorders, and cognitive impairment.

Paroxysmal ocular movements - an early sign in Glut1 deficiency Syndrome

The authors describe a 3-year-old female, diagnosed with GLUT1 deficiency Syndrome, with a previously unreported mutation in exon 7 of the SLC2A1 gene: c.968_972 + 3del P. (Val323Alafs*53), characterized by a classic phenotypic of acquired microcephaly, developmental delay, ataxia, spasticity, and epilepsy. Ketogenic diet was started at the age of 30 months with epilepsy improvement. She presented paroxysmal ocular movements in the first 12 months of life, recently defined as "aberrant gaze saccades", that are present in the early phase of visual system development, being one of the first disease signs, but easily disregarded. Recognizing these particular ocular movements would allow an early diagnosis, followed by ketogenic diet implementation, improving significantly the prognosis and the neurological development of those children.

Glia-neuron energy metabolism in health and diseases: New insights into the role of nervous system metabolic transporters

The brain is, by weight, only 2% the volume of the body and yet it consumes about 20% of the total glucose, suggesting that the energy requirements of the brain are high and that glucose is the primary energy source for the nervous system. Due to this dependence on glucose, brain physiology critically depends on the tight regulation of glucose transport and its metabolism. Glucose transporters ensure efficient glucose uptake by neural cells and contribute to the physiology and pathology of the nervous system. Despite this, a growing body of evidence demonstrates that for the maintenance of several neuronal functions, lactate, rather than glucose, is the preferred energy metabolite in the nervous system. Monocarboxylate transporters play a crucial role in providing metabolic support to axons by functioning as the principal transporters for lactate in the nervous system. Monocarboxylate transporters are also critical for axonal myelination and regeneration. Most importantly, recent studies have demonstrated the central role of glial cells in brain energy metabolism. A close and regulated metabolic conversation between neurons and both astrocytes and oligodendroglia in the central nervous system, or Schwann cells in the peripheral nervous system, has recently been shown to be an important determinant of the metabolism and function of the nervous system. This article reviews the current understanding of the long existing controversies regarding energy substrate and utilization in the nervous system and discusses the role of metabolic transporters in health and diseases of the nervous system.

Inborn Errors of Metabolism with Seizures: Defects of Glycine and Serine Metabolism and Cofactor-Related Disorders

Inborn errors of metabolism (IEM) are relatively uncommon causes for seizures in children; however, they should be considered in the differential diagnosis because several IEM are potentially treatable and seizures can be resolved if appropriate treatment is initiated. Clues from clinical presentation, physical examination, laboratory tests, and brain imaging can raise the possibility of IEM. Several IEM can present with seizures, either as the main presenting finding or as a part of a more complex phenotype. These include cofactor-related disorders, glycine and serine metabolism defects, and other disorders.

Sex-Specific Life Course Changes in the Neuro-Metabolic Phenotype of Glut3 Null Heterozygous Mice: Ketogenic Diet Ameliorates Electroencephalographic Seizures and Improves Sociability

We tested the hypothesis that exposure of glut3+/- mice to a ketogenic diet ameliorates autism-like features, which include aberrant behavior and electrographic seizures. We first investigated the life course sex-specific changes in basal plasma-cerebrospinal fluid (CSF)-brain metabolic profile, brain glucose transport/uptake, glucose and monocarboxylate transporter proteins, and adenosine triphosphate (ATP) in the presence or absence of systemic insulin administration. Glut3+/- male but not female mice (5 months of age) displayed reduced CSF glucose/lactate concentrations with no change in brain Glut1, Mct2, glucose uptake or ATP. Exogenous insulin-induced hypoglycemia increased brain glucose uptake in glut3+/- males alone. Higher plasma-CSF ketones (β-hydroxybutyrate) and lower brain Glut3 in females vs males proved protective in the former while enhancing vulnerability in the latter. As a consequence, increased synaptic proteins (neuroligin4 and SAPAP1) with spontaneous excitatory postsynaptic activity subsequently reduced hippocampal glucose content and increased brain amyloid β1-40 deposition in an age-dependent manner in glut3+/- males but not females (4 to 24 months of age). We then explored the protective effect of a ketogenic diet on ultrasonic vocalization, sociability, spatial learning and memory, and electroencephalogram seizures in male mice (7 days to 6 to 8 months of age) alone. A ketogenic diet partially restored sociability without affecting perturbed vocalization, spatial learning and memory, and reduced seizure events. We conclude that (1) sex-specific and age-dependent perturbations underlie the phenotype of glut3+/- mice, and (2) a ketogenic diet ameliorates seizures caused by increased cortical excitation and improves sociability, but fails to rescue vocalization and cognitive deficits in glut3+/- male mice.

Understanding the Spectrum of SLC2A1-Associated Disorders

Investigators from the Danish Epilepsy Center the frequency of SLC2A1 mutations in a cohort of patients with different types of epilepsies.

A 23 years follow-up study identifies GLUT1 deficiency syndrome initially diagnosed as complicated hereditary spastic paraplegia

Glucose transporter 1 (GLUT1) deficiency syndrome (GLUT1DS) was initially described in the early 90s as a sporadic clinical condition, characterized by seizures, motor and intellectual impairment with variable clinical presentation, and without a known genetic cause. Although causative mutations in SLC2A1 were later identified and much more is known about the disease, it still remains largely underdiagnosed. In the current study, a previously described Italian family was re-analyzed using whole exome sequencing and clinically re-evaluated. Affected individuals presented with spastic paraplegia as a predominant symptom, with epilepsy and intellectual disability, inherited as an autosomal dominant trait with variable clinical presentation. While a novel variant of hereditary spastic paraplegia (HSP) was initially hypothesized in this family, previous linkage studies of known HSP genes did not identify the genetic cause. Exome-sequencing study identified a p.Arg126Cys mutation in the SLC2A1 gene, encoding GLUT1, which segregated with the affected members of the family. The diagnosis of GLUT1DS was further confirmed by cerebrospinal fluid analysis, and treatment was started with good initial response. The description of this large family provides further clinical information on this rare disease. It also offers an example of how GLUT1DS can be challenging to diagnose, and emphasizes the importance of lumbar puncture in the workflow of similar syndromes. Finally, it suggests that analysis of SLC2A1 should be considered in the diagnostic work up of HSP, especially if it is associated with epilepsy.

Atypical Manifestations in Glut1 Deficiency Syndrome

Glucose transporter type 1 deficiency syndrome is a genetically determined, treatable, neurologic disorder that is caused by an insufficient transport of glucose into the brain. It is caused by a mutation in the SCL2A1 gene, which is so far the only known to be associated with this condition. Glucose transporter type 1 deficiency syndrome consists of a wide clinical spectrum that usually presents with cognitive impairment, epilepsy, paroxysmal exercise-induced dyskinesia, acquired microcephaly, hemolytic anemia, gait disturbance, and dyspraxia in different combinations. However, there are other clinical manifestations that we consider equally peculiar but that have so far been poorly described in literature. In this review, supported by a video contribution, we will accurately describe this type of clinical manifestation such as oculogyric crises, weakness, paroxysmal kinesigenic and nonkinesigenic dyskinesia in order to provide an additional instrument for a correct, rapid diagnosis.

The role of SLC2A1 mutations in myoclonic astatic epilepsy and absence epilepsy, and the estimated frequency of GLUT1 deficiency syndrome

The first mutations identified in SLC2A1, encoding the glucose transporter type 1 (GLUT1) protein of the blood-brain barrier, were associated with severe epileptic encephalopathy. Recently, dominant SLC2A1 mutations were found in rare autosomal dominant families with various forms of epilepsy including early onset absence epilepsy (EOAE), myoclonic astatic epilepsy (MAE), and genetic generalized epilepsy (GGE). Our study aimed to investigate the possible role of SLC2A1 in various forms of epilepsy including MAE and absence epilepsy with early onset. We also aimed to estimate the frequency of GLUT1 deficiency syndrome in the Danish population. One hundred twenty patients with MAE, 50 patients with absence epilepsy, and 37 patients with unselected epilepsies, intellectual disability (ID), and/or various movement disorders were screened for mutations in SLC2A1. Mutations in SLC2A1 were detected in 5 (10%) of 50 patients with absence epilepsy, and in one (2.7%) of 37 patient with unselected epilepsies, ID, and/or various movement disorders. None of the 120 MAE patients harbored SLC2A1 mutations. We estimated the frequency of SLC2A1 mutations in the Danish population to be approximately 1:83,000. Our study confirmed the role of SLC2A1 mutations in absence epilepsy with early onset. However, our study failed to support the notion that SLC2A1 aberrations are a cause of MAE without associated features such as movement disorders.

Dietary Treatments and New Therapeutic Perspective in GLUT1 Deficiency Syndrome

OPINION STATEMENT

GLUT1 deficiency syndrome (GLUT1DS) results from impaired glucose transport into the brain: awareness of its wide phenotypic spectrum is a prerequisite in order to ensure an early diagnosis, treating the patients is the subsequent challenge to allow prompt compensation for the brain's lack of fuel. The ketogenic diet (KD) plays a primary role in the treatment of GLUT1DS because it provides ketone bodies as an alternative source to meet the demands of energy of the brain. Therefore, we recommend early initiation of the KD based on the assumption that early diagnosis and treatment improves the long term neurological outcome: the classic KD (4:1 or 3:1) at the present time is the most proven and effective in GLUT1DS. A KD should be continued at least until adolescence, although there are reports of good tolerability even in adulthood, possibly with a less rigorous ratio; in our experience seizure and movement disorder control can be achieved by a 2:1 ketogenic ratio but the relationship between ketosis and neurodevelopmental outcome remains undetermined. Other types of KDs can, therefore, be considered. The Modified Atkins diet, for example, is also well tolerated and provides effective symptom control; furthermore, this diet has the advantage of being easy to prepare and more palatable, which are important requirements for good compliance. Nevertheless, about 20 % of these patients have compliance trouble or the same diet loses its effectiveness over time; for these reasons, new therapeutic strategies are currently under investigation but further studies on pathophysiological mechanisms and potential effects of novel "diets" or "therapies" are needed for this new pathology.

Good outcome in patients with early dietary treatment of GLUT-1 deficiency syndrome: results from a retrospective Norwegian study

AIM

The aim of this study was to characterize patients diagnosed with glucose transporter protein-1 deficiency syndrome (GLUT-1 DS) clinically and genetically, and to evaluate the effect of treatment with the classic ketogenic or modified Atkins diet.

METHOD

We retrospectively studied medical records of 10 patients diagnosed with GLUT-1 DS. Four females and six males with a median age of 15 years were included.

RESULTS

The study illustrates the genetic and clinical heterogeneity of GLUT-1 DS. Analysis of the SLC2A1 gene disclosed a variety of mutation types. The time between onset of symptoms and diagnosis was more than 11 years on average. The outcome in those with early diagnosis and intervention was surprisingly good. All but one patient with the classic phenotype became seizure free after treatment with the classic ketogenic or modified Atkins diet. Acetazolamide was effective in one patient with paroxysmal exercise-induced dyskinesia. A point prevalence of GLUT-1 DS in Norway was estimated as 2.6 per 1,000,000 inhabitants.

INTERPRETATION

Although the long-term prognosis in patients with GLUT-1 DS partly depends on the underlying genetics, our study supports the assumption that early initiation of treatment with a ketogenic diet may positively affect the outcome.

The role of SLC2A1 in early onset and childhood absence epilepsies

Early Onset Absence Epilepsy constitutes an Idiopathic Generalized Epilepsy with absences starting before the age of four years. Mutations in SLC2A1, encoding the glucose transporter, account for approximately 10% of EOAE cases. The role of SLC2A1 mutations in absence epilepsies with a later onset has not been assessed. We found two mutation carriers in 26 EOAE patients, while no mutations were found in 124 probands affected by CAE or JAE.

Glut1 deficiency: when to suspect and how to diagnose?

Impaired glucose transport across the blood-brain barrier results in GLUT1 deficiency syndrome (GLUT1-DS), characterized by infantile seizures, developmental delay, acquired microcephaly, spasticity, ataxia, and hypoglycorrhachia. A part from this classic phenotype, clinical conditions associated with a deficiency of GLUT1 are highly variable and several atypical variants have been described; in particular, patients with movement disorders, but without seizures, with paroxysmal exertion-induced dyskinesia, have been reported. Most patients carry heterozygous de novo mutations in the GLUT1-gene but autosomal dominant and recessive transmission has been identified. Diagnosis is based on low cerebrospinal fluid glucose, in the absence of hypoglycemia, and it is confirmed by molecular analysis of the GLUT1-gene and by glucose uptake studies and immunoreactivity in human erythrocytes. Treatment with a ketogenic diet results in marked improvement of seizures and movement disorders. This review summarizes recent advances in understanding of GLUT1-DS and highlights the diagnostic and therapeutic approach to GLUT1-DS.

Metabolic and monogenic causes of seizures in neonates and young infants

Seizures in neonates or young infants present a frequent diagnostic challenge. After exclusion of acquired causes, disturbances of the internal homeostasis and brain malformations, the physician must evaluate for inborn errors of metabolism and for other non-malformative genetic disorders as the cause of seizures. The metabolic causes can be categorized into disorders of neurotransmitter metabolism, disorders of energy production, and synthetic or catabolic disorders associated with brain malformation, dysfunction and degeneration. Other genetic conditions involve channelopathies, and disorders resulting in abnormal growth, differentiation and formation of neuronal populations. These conditions are important given their potential for treatment and the risk for recurrence in the family. In this paper, we will succinctly review the metabolic and genetic non-malformative causes of seizures in neonates and infants less than 6 months of age. We will then provide differential diagnostic clues and a practical paradigm for their evaluation.

Nonpharmacological treatment of epilepsy

Nonpharmacological treatment of epilepsy includes surgery, vagal nerve stimulation, ketogenic diet, and other alternative/complementary therapies, e.g., yoga, Ayurveda, electroencephalography (EEG) biofeedback technique, aerobic exercise, music therapy, transcranial magnetic stimulation, acupuncture, and herbal remedies (traditional Chinese medicine). Alternative therapies, despite the term, should not be considered as an alternative to antiepileptic medication; they complement accepted drug treatment. Alternative therapies like yoga, through techniques that relax the body and mind, reduce stress, improve seizure control, and also improve quality of life. Ketogenic diet is a safe and effective treatment for intractable epilepsies; it has been recommended since 1921. The diet induces ketosis, which may control seizures. The most successful treatment of epilepsy is with modern antiepileptic drugs, which can achieve control of seizures in 70-80% cases. Patients opt for alternative therapies because they may be dissatisfied with antiepileptic drugs due to their unpleasant side effects, the long duration of treatment, failure to achieve control of seizures, cultural beliefs and, in the case of women, because they wish to get pregnant Surgical treatment may lead to physical and psychological sequelae and is an option only for a minority of patients. This article presents supportive evidence from randomized controlled trials done to assess the benefit of non-pharmacological treatment.

Paroxysmal exercise-induced dyskinesia, writer's cramp, migraine with aura and absence epilepsy in twin brothers with a novel SLC2A1 missense mutation

We report two monochorionic twins that progressively developed, between ages 5 and 10, a combination of episodic neurological disorders including paroxysmal exercise-induced dyskinesia, migraine without or with aura, absence seizures and writer's cramp. CSF/serum glucose ratio was moderately decreased in both patients. Mutational analysis of SLC2A1 gene identified a de novo heterozygous missense mutation in exon 4. This novel mutation has been previously showed to disrupt glucose transport in vitro. Both patients showed immediate and near-complete response to ketogenic diet. This clinical observation suggests that a high index of suspicion for GLUT1 deficiency syndrome is warranted in evaluating patients with multiple neurological paroxysmal events.

GLUT1 deficiency without epilepsy: yet another case

Glucose transporter type 1 (GLUT1) deficiency syndrome is a metabolic disorder characterized by a low cerebrospinal fluid glucose level caused by decreased activity of the glucose transporter protein. Of approximately 100 patients described with this syndrome in the published literature to date, only 3 patients have had intermittent ataxia as the initial manifestation. This case report describes a 13-year-old boy with a longstanding history of intermittent ataxia who was diagnosed as having GLUT1 deficiency syndrome after the onset of seizures at age 11 years. This case highlights the importance of a carefully organized lumbar puncture in the investigation and management of any child with neurodevelopmental delay and intermittent ataxia with or without seizures.

GLUT1 deficiency syndrome--2007 update

GLUT1 deficiency syndrome (GLUT1DS, OMIM 606777) is a treatable epileptic encephalopathy resulting from impaired glucose transport into the brain. The essential biochemical finding is a low glucose concentration in the cerebrospinal fluid (CSF; hypoglycorrhachia; mean 1.7 [SD 0.3mmol/L]) in the setting of normoglycaemia. CSF lactate is normal. Patients present with an early-onset epilepsy resistant to anticonvulsants, developmental delay, and a complex movement disorder. Hypotonic, ataxic, and dystonic features are most prominent. Speech is often severely affected. Some patients develop spasticity and secondary microcephaly. The phenotype is highly variable ranging from severe impairment to children without seizures. Electroencephalography (EEG) may show 2.5-4Hz spike-waves improving on food intake. Neuroimaging is uninformative. Most patients carry heterozygous de novo mutations in the GLUT1 gene (OMIM 138140, gene map locus 1p35-31.3). Autosomal dominant transmission and several mutational hot spots have been identified, but phenotype-genotype correlations are not yet apparent. Homozygous GLUT1 mutations presumably are lethal. The ketogenic diet is the treatment of choice as it provides an alternative fuel to the brain. It should be introduced early and maintained into puberty. Seizures are effectively controlled with the onset of ketosis, but might recur and require comedication. The effect on neurodevelopment appears less impressive. The increasing number of patients, molecular and biochemical analysis, recent research into ketogenic diet mechanisms, and the development of animal models for GLUT1DS have brought substantial insights in disease manifestations and mechanisms. This review summarizes data on 84 published cases and highlights recent advances in understanding this entity.